Ferromagnetic material and method of preparation thereof



FERROMAGNETIC MATERIAL AND METHOD OF PREPARATION THEREOF Lothar Heinrich Brixner, Wilmington, Del., a ssig nor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 14, 1957 Serial No. 665,632

4 Claims. (Cl. 252-625) follows, obviously, that ferromagnetic materials of high coercivity provide better permanent magnet characteristics than those with low coercivity. The ferromagnetic material described in this invention possesses an exceptionally high intrinsic coercive force, and it is represented by the chemical formula SrAlFeO It has a crystalline structure, but this structure is unlike that of such known ferromagnetic materials as the ferrites and BaO-6Fe O The composition of this invention may be prepared by presintering a finely divided mixture of aluminum oxide, strontium carbonate and ferric oxide. The presintered product is cooled and ground to a powder and then compacted into a unitary mass of desired shape by pressing or extruding. The shaped product is then fired at temperatures above about 900 C.

For a clearer understanding of the invention, the fol lowing specific example is given. This example is intended to be merely illustrative of the invention and not in limitation thereof. Unless otherwise specified all parts are by weight.

Example According to the equation:

Al O +2SrCO +Fe O 2SrAlFeO +2CO stoichiometn'c quantities of the reactants (0.6804 part by weight Fe O 0.4353 part by Weight A1 0 and 1.2580 parts by weight SrCO were carefully mixed and finely ground together in an agate mortar to a fineness of 200 mesh. After thorough mixing, the powder was placed in a platinum crucible and heated in air to 800 C. for 6 hours, after which the crucible was taken from the furnace and the reaction product cooled in the crucible to room temperature. The product at this point was a dark brown material which turned olive brown upon grinding to small particle size. A portion of the product was tested with hydrochloric acid for the presence of carbonate and found to be carbonate-free. The material was again ground in an agate mortar to 200 mesh, and the powdered product was pressed into a button /2 inch in diameter under a pressure of 40,000 p.s.i. This button was fired at 1200 C. in air for 8 hours, and cooled. The product obtained was dark brown, and it was useful as a magnet. X-ray analysis showed that it was crystal 2,917,461 Patented Dec. 15, 1959 Saturation magnetization, B gauss 13 Magnetic moment/gram, a ergs/gauss 0.56 Intrinsic coercive force, iH ..oersteds 970 Resistivity ....ohm cm 5 X10 The above value for intrinsic coercive force was obtained when the compoundwas magnetized in an ex ternal field of 2900 oer'st'eds, which proved to be not high enough to saturate the compound. When a mag netizing field of 5500 oersteds was used, the 1H, was 2028 oersteds. These results indicated that the' compound should be magnetized in a field of 7000 to 10,000 oersteds to be saturated.

The above values of the magnetic properties were obtained on a pulverized sample having an apparent density of 1.90 gms./cc. Measurements were made in the following manner. The sample is placed in one of two coils which are matched inductively, and are connected in series opposition with one another, and are in series with a set of variable resistances and a ballistic galvanometer. The test coils are placed inside of a solenoid in such a manner that both are in fields at equal magnitude. A change in the solenoid field causes a corresponding change in the magnetization of the sample which induces a proportional current in the test coil and galvanometer circuit. Calibration against a specimen of known properties permits the measurement of the properties of new materials.

Alternatively, other decomposable compounds might be used as starting materials to produce STAIFCO4- Among these would be Sr(OH) Sr(NO Fe(NO Al(OH) or Al(NO The choice of starting material would be dependent on the purity in which it could be obtained and its cost. Commercially available products of the highest purity are preferred. Although I have chosen to presinter my crystalline material at 800 C. for a period of 6 hours, any temperature between 600 C. and 1000" C. may be used, with time of heating from 4 to 10 hours. Similarly, although the second firing of my crystalline material was carried out at 1200 C. for 8 hours, the temperature for this firing may be from 900 C. to 1400 C. with the time of heating being between 6 and 10 hours.

One of the outstanding advantages offered by the product of this invention is that it can be used to make powerful magnets possessing great resistance to demagnetizing fields, and of minimum size and weight. These magnets may be used in rotating mechanical couplings, television focusing yokes, refrigerator and cabinet door latches, motors and generators.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

I claim:

1. As a new composition of matter, a ferromagnetic material of the chemical formula SrAlFeO 2. A process for preparing a ferromagnetic material which comprises presintering by heating at a temperature from about 600 C.1000 C. for about 4-10 hours a mixture comprising (1) an inorganic strontium compound selected from the group consisting of Sr(OH) Sr(NO and SrCO (2) an inorganic aluminum compound selected from the group consisting of Al(OH) A1 0 and Al(NO and (3) an inorganic iron compound selected from the group consisting of Fe(NO and Fe O said strontium, aluminum and iron compounds being present in the mixture in stoichiometric amounts based on the formation of SrAlFeO 'cooling'the presintered product thus obtained, grinding the product to a powder, compactingthe powder into a unitary mass and heating said mass at a temperature ranging between 900 C.-1400 C. for from 6-10 hours and recovering a ferromagnetic material.

3. A process for preparing a ferromagnetic material which comprises presintering by heating at a temperature from about 600 C.1000 C. vfor about 4-10 hours a mixture comprising SrCO A1 0 and Fe O said'strontium, aluminum and iron componnds being presentin the mixture in stoichiometrie amounts based on the formation rA F Qr w ns he resint r d p q u t h obtained, grinding the product to a powder, compacting he de n a uni ar mess a d a ns m at a temperature ranging between 900 L-"1400 (I. vfor from 6-10 hours and recovering a ferromagnetic material.

4. A process for preparing a ferromagnetic material which comprises presintering by heating at a temperature of about 800 for about 6 hours a mixture comprising SrCO A1 0 and Fe 0 said strontium, aluminum and iron compounds being present in the mixture in stoichiometric amounts based on the formation of SrAlFeO cooling the presintered product thus obtained, grinding the product to a powder, compacting the powder into a unitary mass and heating said mass at a temperature of about 1200 C. for about 8 hours, and recovering a ferromagnetic material.

References Cited in the file of this patent 

1. AS A NEW COMPOSITION OF MATTER, A FERROMAGNETIC MATERIAL OF THE CHEMICAL FORMULA SRAIFEO4.
 4. A PROCESS FOR PREPARING A FERROMAGNETIC MATERIAL WHICH COMPRISES PRESINTERING BY HEATING AT A TEMPERATURE OF ABOUT 800*C. FOR ABOUT 6 HOURS A MIXTURE COMPRISING SRCO3, AI2O3, AND FE2O3, SAID STRONTIUM, ALUMINUM AND IRON COMPOUNDS BEING PRESENT IN THE MIXTURE IN STOICHIOMETRIC AMOUNTS BASED ON THE FORMATION OF SRAIFEO4, COOLING THE PRESINTERED PRODUCT THUS OBTAINED, GRINDING THE PRODUCT TO A POWDER, COMPACTING THE POWDER INTO A UNITARY MASS AND HEATING SAID MASS AT A TEMPERATURE OF ABOUT 1200*C. FOR ABOUT 8 HOURS, AND RECOVERING A FERROMAGNETIC MATERIAL. 